Modeling transient flow behavior of a horizontal well in a coal seam

CBM is an important unconventional energy resource with continuing interest in research and development. Based on Langmuir adsorption isotherm and pseudo-steady diffusion in matrix and Darcy flow in the network of cleats, and treating the media directly connected with horizontal wellbore as the network of cleats, we established a model of CBM horizontal well production and the partial differential equations were solved by the method of Laplace transform. Later in the paper, we obtained the standard log–log type curves of pressure transient and rate decline analysis using numerical simulation and analyzed the transient transport behavior thoroughly. The numerical simulation results showed that the type curves are the typical response of CBM horizontal well production. We also showed that type curves characteristics are affected by external boundary conditions, transfer coefficient, storage coefficient and adsorption coefficient, etc. At the end, we showed the differences of our CBM horizontal well model with the CBM vertical well model and the dual porosity non-coal reservoir models. The research results show that our model would be a good semi-analytical model to make well test interpretations in real case studies.

► The physical phenomena of desorption, diffusion and flow were considered and descripted.
► The effect of top, bottom and side boundaries on rate and pressure transients was modeled and analyzed.
► The effect of property parameters on rate and pressure transients was modeled and analyzed.
► The difference of CBM wells with non-coal wells was compared.
► The applicability of the researched model to water-producing CBM reservoirs was discussed.